Metadata

Metadata is data on data, or data about data. Databases are made up of not only the actual data, but also
Information on the data, such as what kind of data is stored, what kind of attributes they have, or how they relate to each other. In DBMS, this information is stored in different schemas.
In relational DBMS the most important schema is the conceptual schema which represents the relations between each entity. For example, in a database storing employee information for a company, we might have relations like:
-each employee has one manager
-each manager has one or more employee
-each manager has one department
-each department has one or more employee
And so on
Even though the schema is in the strictest form in text form, the term is now often used for the graphical representation.

sources/further reading:
http://en.wikipedia.org/wiki/Database_schema
http://en.wikipedia.org/wiki/Metadata